The present invention relates to measuring skew between signals transmitted on two conductors, and more specifically, to tuning a testing apparatus used to measure the skew.
A testing apparatus such as a time-domain reflectometer (TDR) may be used to measure skew between signals transmitted on two conductors. Generally, skew is a misalignment of signals propagating in a conductive material. Skew may be caused by many different factors such as wire-interconnect length, temperature variations, variation in intermediate device, capacitive coupling, material imperfections, and the like. Cable vendors may use a TDR to test skew in cables that include multiple conductors. The skew caused by the cables represents the misalignment between signals that are transmitted on one end of the conductors at the same time but arrive at different times at the opposite ends of the conductors. Accurately measuring skew is important for many applications such as transmitting differential signals or data and clock signal synchronization.
When testing skew using a TDR, the characteristics of the signal used to measure the skew are important. For example, the frequency and power at which the TDR drives a signal onto a cable affect the skew measurement. Typically, cable vendors use the same standardized testing signal to determine the skew of a cable regardless of the intended use of the cable—e.g., the type of data, the frequency of the data signals, the power used to drive the data signals, and the like.